<body></body>
<title>a page with an iframe</title>
<!-- This page makes an iframe to |subframe_url|.-->
<script>
const url_params = new URLSearchParams(location.search);
let subframe_url = url_params.get("subframe_url");
if (subframe_url != null) {
  let iframe = document.createElement('iframe');
  iframe.src = subframe_url;
  iframe.name = "subframe_name";
  document.body.appendChild(iframe);
}
</script>
